For information, a kruger nose is a hypersupporting device in the shape of a flap which retracts during the flight so as to form an intrados or a lower side region of the leading edge of the wing. During taking-off or landing, this flap is deployed by a mechanism housed in the leading edge so as to increase lift by extending towards the front extrados or top surface of the wing.
Although this application does not need to be regarded as restrictive, the use of kruer noses on the leading edge of the wings of aircraft is particularly adapted to the case of hybrid laminar wings in which a layer suction system is placed on the top side of the leading edge. In fact, this technique requires that there is no irregularity on the extrados of the leading edge, which is precisely possible by using kruger noses as hypersupporting devices.
As illustrated in detail in the document U.S. Pat. No. 4,398,688, the latter describes kruger noses including rigid flaps, generally articulated, and deployed by means of a single pivoting around a fixed spindle.
However, these rigid kruger noses comprise either a single deployed position in which a slot may be provided between the flap and the leading edge, or several deployed positions without any slot.
Existing rigid kruger noses thus do not take into account certain contradictory requirements of the landing and take-off stages.
Thus, it is desirable in the landing phase to define an intermediate position in which the flaps of the kruger noses are orientated according to a clearly specific angle (about 65 degrees) with respect to the median plane of the wing and in which a slot with a specific width (for example about 1% of the cord of the wing) is formed between the flap and the leading edge. In fact, this configuration is favorable for obtaining a maximum lift level essential for this flight phase.
Moreover, in the extreme take-off position, which corresponds in this case to a specific orientation of the flaps of the kruger noses (for example about 30 degrees with respect to the median plane of the wing), it is on the other hand desirable that no slot exists between these flaps and the leading edge. In fact, the absence of any slot during take-off is generally favorable for good fineness of the wing and in addition is better able to protect the leading edge from any possible impacts (insects, dust, etc) by suppressing the separation line of the fixed leading edge. This absence of any slot is even more favorable in a laminar wing as the presence of several insects or dust remaining glued to the leading edge is likely to destroy the laminarity throughout the next flight phase, even if a cleaning system is provided.
As illustrated in detail in the document U.S. Pat. No. 3,743,219, there are also deformable kruger noses including a flap whose shape is modified by the mechanism, which ensures its deployment between its folded back position and its deployed position. The advantage of this conception is to enable the flap to be adapted to the shape of the lower profile of the wing when the flap is folded back and to the aerodynamic requirements when the flap is deployed.
Furthermore, the document U.S. Pat. No. 3,743,219 describes a kruger nose whose deployment mechanism makes the flap move through an intermediate landing position in which a slot is formed between the flap and the leading edge before reaching the fully deployed take-off position in which there is no slot between the flap and the leading edge.
However, the mechanism ensuring deployment of the flap and the ensuing kinematics are complicated by the deformable nature of the flap.
In addition, the de-icing of these deformable flaps has to be effected via the blowing of hot air from the leading edge of the wing. If this wing has a laminar profile, which assumes as seen that suction is carried out on the top surface or extrados of the leading edge, this particular solution cannot in practice be used.